Circuit for radio communication



Ma 17, 1932. R N UBL 1,859,016

CIRCUIT FOR RADIO COMMUNICATION Filed March 16, 1929 INVEN TOR. ZoBEkT /V/L 11625 BYW ATTORNEYS.

Patented May 17, 1932 UNITED STATES ROBERT NEIL AUBLE, OF INDIANAPOLIS, INDIANA CIRCUIT FOR RADIO COMMUNICATION Application filed March 16, 1929. Serial No. 347,495.

This invention relates to an improved circuit for radio communication and more particularly to a circuit in which a thermionic vacuum tube is used for amplification of the signals.

One of the objects of the invention is to provide a circuit in which there is no inherent tendency to oscillation'dueto the inter-element capacity in the vacuum tube.

Another object of the invention is to in crease: the amplification which can be obtained for a given tube at a given plate potent-ial without distortion.

Another object of the invention is to pro- 1 vide a circuit in which either alternating or direct current may beused for heating the cathode of the vacuum tube.

Another object of the invention is to provide a circuit in which no direct current is taken by the grid electrode of the vacuum tube.

One feature of the invention resides in the fact that there is no conductiveconnection between the grid electrode and either of the other electrodes of the tube.

Another feature resides in the fact that the connection between the input circuit of the vacuum tube and the output circuit is completed through a condenser..

Other objects and features of the invention will be understood from the following specifications and claims and the attached wiring diagrams; In the diagrams, Fig. 1 shows an application of the invention to a radio receiving apparatus consisting ofa single stage of radio frequency amplification and a detector stage. Fig; 2- illustrates the application-of the invention in a two-stage radio frequency amplifier coupled to a standard detector tube circuit and two stages of transformer coupled audio frequency amplification. Fig. 3 shows the invention in a circuit wherein the cathode is heated by alternating current from a suitable transformer connectedto public service power lines. Figs. 4 and 5 show further modifications of circuits in which the invention isused. In the drawings an antenna 10 is connected to the primary of the-usual type of radio frequency transformer 11 which in turn is grounded at 12. The secondary of the transformer 11 is connected in parallel with the tuning condenser 13 and one end is connected to the grid 14 of a thermionic vacuum tube 65 15. The opposite ends of the secondary of the transformer 11 and the condenser13'are connected to one plate of a condenser 16. p The opposite plate of the condenser 16 is connected in turn to one side of the primary of the transformer 17 and to the positive terminal of the usual B-battery 18. The plate electrode19 of the thermionic tube 15 is connected tothe opposite side of the primary of the transformer 17 The filament or cathode 20 of the tube 15 is heated by the usual A-battery' 21 connected in the usual manner without regard to polarity as shown in the diagram. ,By this connection the input circuit or grid circuit of the tube is connected to the output circuit or plate circuit through the condenser 16 and there is no conductive connection between the grid and either the filament or plate.

. The detector circuit shown in Fig.1 is a standard detector circuit and consists of the thermionic tube 22, grid condenser 23, grid leak 24, the secondary of the transformer'17, the tuning condenser 25, the usualA- and B-batteries 26 and 27 and the output connec- 9 tions 28 to which may be connected the usual ear phones, loud speaker or audio amplification circuits. .Any practical'form of detec tor circuit and audio amplification circuit might be used. V 4

For convenience in this diagram, the audio frequency circuitand the detector circuit are shown using separate batteries instead of the more common method of usingthe same batteries for. both circuits. V

In Fig. 2 is shown a radio receiving circuit A using two stages of radio frequency amplification indicated generally by the numbers 29 and 30. Each of these stages is exactly similar to the radio frequency amplification stage described for Fig. 1, the. output of stage 29 being coupled to the input of stage, 30 through the transformer 31.

The remainder of the circuit in Fig. 2 consists of a standard detector circuit indicate at 32 and two stages of standard audio frequency amplification 33 and 34 which will not be described in detail.

In the radio frequency circuits in the two Figures 1 and 2, there is no inherent tendency to oscillation since there is no conductive connection whatever between the grid and the plate of the tube. The grid is free to adjust itself automatically to a potential dependent upon the action within the tube itself and it has been found by experience that the potential so assumed gives much greater amplifi cation for a given plate potential with less distortion of signals than has been possible with any fixed grid bias The condenser 16 may be set at a value which gives excellent results over a great range of frequency. The condenser value is not a critical factor, being itself variable between wide limits without affecting the stability of the circuit. If the condenser 16 is made variable, the amplification for a given frequency may be considerably varied. This provides a convenient method of volume control and allows the filament current to be maintained at a constant value instead of being varied to provide the desired variations in volume. This has the advantage of allowing the filament temperature to be maintained at the proper position for maximum efficiency of the tube.

An alternating current may be used to heat the tube filament as shown in Fig. 3 wherein a suitable transformer 37 has its primary winding connected to public service power lines 38 and 39 and its secondary winding connected to the filament electrode as shown. The mid-point of the secondary winding is connected to ground.- Thus, when the B- battery negative terminal is also connected to ground, as is common practice, there is no change incircuit for adaptation to either alternating or direct current.

In Figs. 4 and 5 inductive choke coils 36 are connected between the condenser 16 and the transformer l'l'. These provide a means of adjusting the coupling of transformer 17 so that a standard transformer with fixed coupling may be used. If a transformer of proper coupling originally chosen, the choke coils are unnecessary. 1

The invention claimed is:

1. A radio" frequency amplification circuit including a thermionic tube having filament, grid and plate electrodes, a source of electric potential for heating said filament, an input transformer having one terminal of its secondary winding connected to said grid electrode, a tuning condenser connected in parallel with the secondary winding of said input transformer and having no conductive connection with the filament electrode, a second condenser having one terminal connected to the second terminal of the input transformer,

an output transformer having one terminal of its primary winding connected to said plate electrode and the opposite terminal of its primary winding connected to the second terminal of said second condenser, and a source of electric potential having one terminal connected to the second terminal of the primary winding of said output transformer and its other terminal connected to said filament electrode.

2. A radio frequency amplification circuit comprising a thermionic tube having filament, grid and plate'electrodes; a source of electric potential for heating said filament; an input circuit including the said grid elec- .trode, the secondary winding of an input transformer, a tuning condenser and one plate of a second condenser; an output circuit including the said plate electrode, the primary winding of an output transformer, a source of electric potential, and the said filament electrode; and aconnection between the opposite plate of the second-mentioned condenser and a point in said output circuit, said connection including an inductive choke coil.

3. A radio frequency amplification circuit including a thermionic tube having filament, grid and plate electrodes, a source of electric potential for heating said filament, an input circuit connected to said grid and including a tuning condenser having no conductive connection to said filament or plate, an output circuit including an output transformer having one terminal of its primary winding connected. to said plate electrode, and a second source of electric potential having one terminal connected to the second primary terminal of said output transformer and its second terminal connected to said filament and a condenser having only one terminal connected to said input circuit and the opposite terminal connected to a point in the output circuit between said output transformer and said second source of electric potential.

4. A radio frequency amplification circuit including a thermionic tube having filament, grid and plate electrodes, a source of electric potential for heating said filament, an input circuit connected to said grid and including a tuning condenser having no conductive connection to said filament or plate, an output circuit including an output transformer having one terminal of its primary winding connected to said plate electrode, and a second source of electric potential having one terminal connected to the second primary terminal of said output transformer and its second terminal connected to said filament and acondenser having only one terminal connected to said input circuit and the opposite terminal connected to a point in the output circuit between said output transformer and said filament. I

5. A radio frequency amplification circuit including a thermionic tube having filament, grid andplate electrodes, a source of electric potential for heating said filament, an input circuit connected to said grid and including a tuning condenser having no conductive connection to said filament or plate, an output circuit including an output transformer having one terminal of its primary Winding connected to said plate electrode, and a second source of electric potential having one terminal connected to the second primary terminal of said output transformer and its second terminal connected to said filament and a condenser having only one terminal connected to said input circuit and the opposite terminal connected to a point in the output circuit between said output transformer and said second source of electric potential, said condenser being variable to provide volume control.

6. A radio frequency amplification circuit including a thermionic tube having filament, grid and plate electrodes, a source of electric potential for heating said filament, an input circuit connected to said grid and including a tuning condenser having no conductive connection to said filament or plate, an output circuit including an output transformer having one terminal of its primary Winding connected to said plate electrode, and a second source of electric potential having one terminal connected to the second primary terminal of said output transformer and its second terminal connected to said filament and a condenser having only one terminal connected to said input circuit and the opposite terminal connected to a point in the output circuit between said output transformer and said filament, said condenser being variable to provide volume control.

In Witness whereof, I have hereunto affixed my signature.

ROBERT NEIL AUBLE. 

